1. Field of the Invention
The present invention relates to a device and method for controlling the startup of a fuel cell system.
2. Description of Related Art
A fuel cell is a device that directly converts chemical energy of a fuel into electrical energy by allowing reactant gases (namely, an anode gas such as hydrogen and a cathode gas such as air) to electrochemically react with each other. Such fuel cells are classified into various types of fuel cells in accordance with, for example, the type of electrolyte used. One type of fuel cell is a solid polymer electrolyte fuel cell in which a solid polymer electrolyte is used as the electrolyte.
In a solid polymer electrolyte fuel cell, the following catalytic electrode reactions are carried out in an anode electrode and a cathode electrode.Anode electrode: 2H2→4H++4e−  (1)Cathode electrode: 4H++4e−+O2→2H2O  (2)
In this manner, when an anode gas (H2) is supplied to the anode electrode, the reaction represented by formula (1) is carried out to produce hydrogen ions (H+). The resulting hydrogen ions (H+) permeate through (diffuse into) an electrolyte (e.g., a solid polymer electrolyte membrane in the case of a solid polymer electrolyte fuel cell) in a hydrated state and reach the cathode electrode. The reaction represented by formula (2) is then carried out using the hydrogen ions together with a cathode gas (for example, air) supplied to the cathode electrode. The reactions represented by formulas (1) and (2) are carried out in the electrodes, and thus the fuel cell generates electricity which may be used for motive force. The electricity commonly generated by a typical fuel cell is at about 1 volt. Consequently, in order to use fuel cells as a power source of an automobile, a plurality of fuel cells are provided in the form of a fuel cell stack in which several hundred fuel cells are stacked together in series. In addition, in order to use fuel cells as a power source of an automobile, it is desirable that the fuel cell system be capable of being rapidly started in any ambient environment.
As represented by formula (2), a fuel cell produces moisture (H2O) in the cathode electrode concurrently with the power generation. When the operation of a fuel cell is stopped in an environment at a temperature below the freezing point, and the fuel cell is unused for a period and then started at a temperature below the freezing point, the water produced may be in a state in which the water is frozen on an electrode catalyst or a gas diffusion layer adjacent to the electrode catalyst. In such a state, the electrode reaction area is decreased, thereby significantly degrading the ability of a reactant gas to diffuse to the electrode catalyst. In such a case, it is known in the art that by increasing the gas pressure of a reactant gas supplied to the fuel cell stack, the reactant gas is more consistently able to reach a reaction site where a catalytic electrode reaction occurs.